The present invention relates to optical sensors for pointing devices, such as mice and trackballs. In particular, it relates to the reduction of the number of components.
Typically, mice and trackballs have a ball which is either rolled across a desktop when a user moves the mouse, or is manipulated with a user""s finger for a trackball. This motion is detected in both the x and y directions by the use of two rollers which are biased against the ball inside the device. The rollers are offset from each other at an angle of 90xc2x0. Each roller will typically have a shaft connected to an encoder wheel, which is a wheel with a number of slots. A light emitter, such as a light emitting diode (LED) is mounted on one side of each encoder wheel, with one or more photodetectors on the other side. Multiple photodetectors may be used for differential detection. When the encoder wheel turns, light alternately passes through the slots, and is blocked by the encoder wheel, allowing a determination of the amount of movement of the ball in the x or y direction.
Newer mice and track balls will sometimes include a separate roller wheel which the user can manipulate for scrolling. Such a roller wheel is typically also connected to a separate encoder wheel, which also has an emitter and a detector on either side for determining its movement.
Another typical input for mice and trackballs is one or more buttons to indicate a clicking function. The buttons are typically spring biased to allow the user to depress them, and then have them pop back up. The buttons will typically depress a microswitch mounted beneath the button to provide an input signal. Each button typically has its own microswitch.
One of the challenges in the design of such pointing devices is the reduction of costs and reductions in size, or fitting additional functionality in the same size device. One obvious way to reduce costs is to reduce the number of components required to build the mouse or trackball or other pointing device.
The present invention provides a method and apparatus for eliminating at least one light emitter and one light detector in a mouse design. This is done by using two conical shaped encoder wheels positioned so that they are almost touching each other. A single light emitter then is used to shine light at the junction, so that it strikes both cones. Adjacently located is a single chip, integrating two groups of photodetectors. The chip is positioned so that light directed at the first conical encoder impinges on the first group of photodetectors, while light directed at the second conical encoder impinges on the second group of photodetectors. Thus, the two photodetectors can be integrated on a single chip, saving a separate photodetector chip. In addition, only a single LED is required.
In a preferred embodiment, encoder wheels are connected to rollers which contact the ball at 90xc2x0. The encoders are conically shaped with a cone angle of 45xc2x0. The semiconductor chip with the photosensors is mounted in the vertical plane tangent to both conical shaped encoders. The encoders alternately block and let light pass through as they rotate with their respective roller. This embodiment is referred to as a transmissive embodiment, since light passes through the encoders.
In an alternate embodiment, conical shaped encoders having a reflective surface, instead of the slots used in the more typical transmissive encoders, are used. In this alternate embodiment, the conical encoder selectively reflects light directed at it, by the LED placed in front of it, to a detector which is also placed in front of the conical encoder disk-the same side as the LED. In this embodiment, the detector can be placed on the PCB in the vertical plane, tangent to both conical shaped encoders, or it can be mounted at any angle ranging from horizontally flat to vertical on the PCB, or at any angle in this range relative to reflected light to adequately receive the reflected light.
The primary advantage of the reflective scheme over a transmissive one in the present invention is the reduction in interference between non-encoded and encoded light. Non-encoded light is direct light from the LED, and encoded light is light after it has interacted with the encoder disk. In a transmissive system, the potential does exist for the photodetector to receive non-encoded light, xe2x80x94i.e. light that goes directly from the LED to the photodetector, and hence introduce inaccuracies in coordinate detection. Ideally, the photodetector should receive nothing but encoded light. The inaccuracies are introduced because the non-encoded light decreases the amplitude of the modulated signals. As the signal amplitude or the signal quality is reduced, it gets more difficult and more expensive to detect each light pulse. The reflective scheme, by not placing the photodetector in the direct path of the LED, aims to ensure that the photodetector sees only encoded light. Thus, the reflective scheme reduces optical interference between non-encoded and encoded light, and hence improves the detection accuracy of the device. Another advantage of the reflective system is that the encoder disks have no slots, and are therefore easier and less costly to mold.
In yet another alternate embodiment, a controller or application specific integrated circuit (ASIC) for the pointing device can also be integrated on the same semiconductor chip as the photosensor. This further reduces the part count by combining these two chips into one.
In an additional embodiment, a set of (2-4) light pipes can be used to direct light to a third group of photodetectors on the semiconductor chip, thus eliminating another photosensor chip. The proper implementation of light pipes requires at least one light pipe per each light sensitive area. The third group of photodetectors could be used to detect light directed at an encoder wheel connected to a roller for scrolling. Alternately, light could be used to detect the depression of a button, rather than the microswitch. Thus, one or more light pipes can connect to multiple sensors on the same chip. As used herein, the terms xe2x80x9csensorxe2x80x9d or a xe2x80x9cphoto sensorxe2x80x9d terms xe2x80x9cdetectorxe2x80x9d or xe2x80x9cphotodetector.xe2x80x9d Also the term xe2x80x9csensorxe2x80x9d is intended to refer to a single sensor and or a group of sensors.
For further understanding of the nature and advantages of the invention, reference should be made to the following description taken in conjunction with the accompanying drawings.